The activities of the Biomathematics unit will be essential for maximizing the yield of useful information from the scientific/clinical projects in this Photodynamic Therapy Program. An objective, quantitative approach to basic and clinical research is especially relevant when the systems under study are complex and when program goals demand the integrated participation of several scientists, for example, when PS (photosensitizers) are synthesized by Project 1, then screened in Core A, then studied in detail in Projects 2 and 3, and possibly tested clinically in Project 4. Although collaborations are primarily initiated by other researchers in the Program, the Biomathematics Unit, in its effort to identify useful quantitative techniques may also initiate collaborations. After identifying useful, quantitative biomathematical techniques, they are checked, corrected if necessary, extended if potentially fruitful, implemented into specific tools and used to facilitate a deeper understanding of complex photodynamic, pharmacokinetic and cellular kinetic systems. Laboratory and clinical scientists can obtain the use of biomathematical expertise, advice and use of custom and commercial computer software and hardware, and tutorials and advice on varying depth on biomathematical topics by communicating their need to the Biomathematics Unit. Collaborations ca ranges from a five minute conversation to multiyear multiproject programs. Specific aims include. 1.Mathematical models, usually empirical or semi-empirical, will be adapted from the literature, or created, as needed. Routine standardized data analyses procedures will be implemented in specific labs. Results from routine use will be reviewed. 2.Specific individual databases will be set up for specific projects. Joint central databases will be set up where needed. Databases will be updated and adapted to changing requirements of specific projects. 3.Seminars on Biomathematics topics will be given. Tutorials on software and/or data analysis techniques and principles will be provided where needed. Results will be presented at scientific meetings. Results will be published in scientific journals. 4.Minor installations, improvements and repairs, will be made to computer software/hardware systems.